The present invention relates to a method and a cutting insert for threading. The method aims to produce a thread in a rotary work piece, wherein a threading insert, including at least two cutting tips, creates the shape of the thread through a number of passes along the work piece. The invention further relates to a threading insert.
At threading in a turning operation cutting inserts are often used which consist of an insert body including one or more cutting edges. Typical for these cutting edges are that they are geometrically designed such that they can generate a thread on a rotary work piece through chip removing machining. The threads which are made thereby obtain a certain profile, for example ISO, UN, Whitworth etc., and they have a pitch. Conventional threading inserts of the full profile insert type are constructed such that the cutting edge comprises a thread profile, whose largest width is identical to the pitch and whose cutting insert tip form for example a 60xc2x0 profile angle. A threading insert of this type has its weakest point at the outermost part of the cutting insert tip. That depends on that the tip is submitted to the largest strain at conventional threading, by having the extreme tip portion cutting during all passes until full depth of thread.
It is previously known through for example U.S. Pat. No. 4,575,888 to provide a number of cutting tips on the same cutting corner to reduce the number of passes until obtaining the finished thread. The possibilities to use such an insert with multiple teeth are however limited since they require a large thread clearance and rigid working conditions since the long active cutting edge will lead to large cutting forces.
At flank infeed a chip is obtained with a rectangular cross section, which is easy to shape and to manage in comparison with a chip from the radial infeed, when the chip may assume a rigid V-shaped cross section. This fact together with a more efficient heat deduction from the cutting insert corner makes it possible to work with larger chip thickness and to complete the thread with the same number of passes as by radial infeed. When a conventional threading insert is fed parallel with one flank of the thread, the cutting edge however abutting against the same flank will not produce any intrinsic cutting work but will only drag along the flank, which will have an abrasive effect on the cutting edge and which can give bad surface finish on the thread flank. One has tried to feed the cutting insert tip at an angle which is smaller than the flank angle for avoiding these negative effects but then obtained chips from the side of the minor cutting edge which have been thin and entangled, which have influenced tool life and surface finish.
One object of the present invention is to provide a threading insert which combines the good properties of radial infeed and flank infeed, that is, the practical simple method with radial infeed is combined with good chip control from flank infeed.
Another object of the present invention is to provide a multiple teethed threading insert, which does not require a large thread clearance in the work piece or extremely rigid working condition.
Another object of the present invention is to provide a threading insert, which obtains a good tool life by having several cutting tips dividing the work load.
Another object of the present invention is to provide a threading insert, which reduces the time for processing at threading.
Still another object of the present invention is to provide a method for producing a thread while having good production economy.